with a grade sufficient to insure easy handling of the loaded

cars.

The empty cars are taken around behind the loaded cars into a back-switch, or they may be shifted by a truck, as shown by Atlas Sheet No. XV. A back-switch is for many reasons preferable to a transfer truck, but requires much more space than the latter. The truck at the Hollenback breaker was added after the breaker was built. This accounts for the presence of the deflection sheave shown by Atlas Sheet No. XVI.

When a loaded car is raised, the empty car standing on the truck is started, and, running down the grade, collides with the former, starting it down towards the dump. The empty car runs upon the cage, is locked in place, and lowered into the mine while the loaded car is being dumped. As soon as the car is emptied it is hooked to the rope by a chain, as shown at j, the lever a is thrown forward or backward as the case may be, throwingƒ or f' into gear, thus communicating motion to the drum c. The car is hauled (up grade) by the rope along the side track s or g and run upon the truck.

The truck is then moved over by means of the lever b, the bevel gear l, k, and the rack (m) and pinion, until the car stands immediately behind the compartment from which it was raised.

The latches at p, and on the track x are spring switches; the latches at g remain in the position shown except when a car containing rock, slate, or other refuse is raised, when the car is back-switched through g to the rock dump.

This is not the plan usually adopted for handling the refuse. Cars filled with refuse are seldom raised to the top of the breaker, but are commonly taken off at a landing level with the ground, or with the culm car tracks.

The illustration (Plate XV) shows the course of the rope around small sheaves at d, e, i, etc.

The levers n and n' operate the cage rests (keeps, wings) for the two compartments, as shown at r, r.

Shute linings.-The main shute into which the coal is first dumped, (when not dumped directly on the bars.) the

BREAKER in PROCESS of CONSTRUCTION, KOHINOOR COLLIERY

lump coal and steamboat shutes, the shute leading from beneath the bars to the mud screen, and in general all shutes in which large coal is handled, require stout plate-iron linings. When the coal is wet and the water very acid, castiron plates are occasionally used, but the most common plan is to line with wrought-iron plates.

The main dump shute, steamboat, and lump shutes, are not infrequently lined with heavy strap-iron placed as closely as possible to cover the entire bottom of the shute, the sides being lined with plate iron.

Hoppers, shutes, and telegraphs in breakers preparing dirty wet coal that must be washed and jigged with strong mine water, are made of cast-iron three-fourths to one-and a-quarter inches thick. In the Panther Creek district plates of this thickness are often destroyed by the mine water in one year.

Breakers preparing dry coal have their hoppers, shutes, and telegraphs lined with sheet-iron plates.

Screen Bars.

The "screen bars," "bars," or "grate bars," are made of various forms.

The object of screening over bars is to separate, at once, coal already broken down to comparatively small sizes and the finer material not marketable, so that the remainder shall consist only of large pieces. To accomplish this thoroughly, it is evident that the coal should run freely over the bars, and that the bars should never become clogged up.

Bars made flat on top do not accomplish this object as thoroughly as pointed or rounded bars, because on a flat bar the fine fragments have no special tendency to run into the apertures between the bars.

Bars made with a diamond shaped (flat pointed) head, probably screen the coal better than any other form, and do not readily become clogged up; but when the coal is dumped from the car directly upon the bars, this form is not admissible, as it increases the amount of fine coal.

Bars with a rounded head (top) are probably better than any other form when the coal is dumped from the car di

rectly upon the bars, but they are more likely to become clogged than pointed bars.

When the coal is run out upon the bars under a gate from a shute or pocket, the latter form is probably the best that can be adopted.

They are usually arranged in steps, as shown by Atlas Sheet No. XVI.,* so that the coal in passing from one set to the set below, falls one, two, or three inches. This fall jars the coal, the lumps roll over, and the dust and fine coal are shaken off.

Each set is made from three to five feet long, and the bars are seated on fluted plates, the fluting, or grooves, being about half an inch apart, so that the space between the bars may be changed at will, by seating them in grooves a certain distance apart.

They have generally been made of cast-iron, but wroughtiron and steel bars have lately been used. Ordinary rails without the bottom flange, make a very good form of bar for separating out the lump, but they do not answer as well for smaller sizes.

A thorough separation of the dirt and smaller sizes of coal from steamboat and lump, cannot be effected unless the coal is fed slowly and regularly. When a car load of coal is dumped directly upon the bars, a considerable quantity of small coal and dirt is sure to be forced over the bars upon the platform, unless the bars are very long; and even in this latter case, when several car loads are dumped in quick succession, the bars almost surely become more or less clogged up, and the separation is very imperfect.

These defects are almost entirely overcome by dumping the coal into a shute sufficiently large to hold two or three car loads of coal, and feeding the coal out slowly under a gate.

An improved form of screen bar, or rather a mechanical substitute for the screen bars, has lately been adopted by Mr. Eckley B. Coxe.

It is shown by Fig. 1 on Atlas Sheet No. XX, and consists of two frames, each carrying a set of narrow bars. * See also Atlas Plate No. XVIII, C, C', C'.